1. Field of the Invention
The present invention relates to a room temperature curable silicone rubber composition, and specifically to a condensation type room temperature curable silicone rubber composition, and a mold material formed from such a composition.
2. Description of the Prior Art
Condensation curable room temperature curable compositions cure at room temperature to form an elastomeric cured product, and are widely used in a variety of applications including insulating materials, sealing materials, potting materials, molding matrix materials, and tampo printing materials.
In particular, two part type condensation curable compositions are used for molding matrix materials and the like, although in order to enable such compositions to be used in practical applications, they must be provided with an appropriate usable lifetime (or pot life). If the composition does not have a suitable pot life, then curing begins before the composition can be formed into the desired shape, or before the composition can be used to fill a suitable mold, making the practical application of the composition essentially impossible.
However, in conventionally used two part type condensation curable compositions, in which a mixture of an organopolysiloxane and a reinforcing fine silica powder is used as the principal constituent, the pot life is generally short, meaning the curing reaction begins to progress and the viscosity increases during working of the composition, and as a result, these compositions can be difficult to use in practical applications. Furthermore, in those cases where such compositions are used as mold materials, the resulting mold durability relative to urethane resins has been unsatisfactory.
Moreover, Japanese Laid-open publication (kokai) No. 7-41562 (JP7-41562A) discloses a method of producing a liquid silicone rubber composition using a high bulk density silica, although no mention is made of a room temperature (condensation) curable composition. Furthermore, Japanese Laid-open publication (kokai) No. 11-256040 (JP11-256040A) discloses a method of producing a mixture (a base compound) of a silicic acid with a high tap density and a silicone polymer, although no specific description is given of the composition.
The present invention aims to resolve the problems described above, with an object of providing a room temperature curable silicone rubber composition for which any increase in viscosity over time is suppressed, and which has a pot life that enables adequate workability, and an improved mold durability relative to urethane resins.
The present invention achieves the aforementioned object, with a first aspect that provides a room temperature curable silicone rubber composition comprising:
(A) 100 parts by weight of an organopolysiloxane represented by a general formula (I) shown below, with a viscosity at 25xc2x0 C. of 100 to 500,000 mm2/s, 
xe2x80x83wherein, each R1 represents, independently, a substituted or unsubstituted monovalent hydrocarbon group, and n represents a number which results in a viscosity at 25xc2x0 C. of 100 to 500,000 mm2/s,
(B) 1 to 100 parts by weight of a surface-treated reinforcing fine silica powder with a specific surface area as measured by a BET method of at least 50 m2/g, and a tap density of 0.2 to 0.4 g/ml, which has undergone treatment with an organosilicon compound to produce a quantity of surface carbon of at least 2.5% by weight, and
(C) 0.01 to 10 parts by weight of a tin compound-based curing catalyst.
Furthermore a second aspect of the present invention provides a mold material produced from a composition as described above.